Diesel engines fuelled with gaseous fuel, such as natural gas, can operate at comparable power and efficiency as when fuelled with diesel fuel, but at lower emissions and cost. Gaseous fuel is introduced later in the compression stroke (“late-cycle”) and forms a stratified charge that burns in a diffusion combustion mode. The temperature and pressure within the combustion chamber at the end of the compression stroke is not suitable for auto-igniting the gaseous fuel when using conventional compression ratios employed in diesel engines. It is typical to employ a pilot fuel as an ignition mechanism for the gaseous fuel. A relatively small amount of the pilot fuel is injected into the combustion chamber, where the temperature and pressure are suitable for its ignition, and the combustion of the pilot fuel acts as a high energy ignition source for the gaseous fuel. It is a challenge to introduce both the gaseous fuel and pilot fuel late-cycle in engines where there is limited space in the cylinder head. In some applications there is not enough space in the cylinder head for installing separate gaseous fuel and pilot fuel injectors. This problem has been solved generally by two different techniques for integrating a gaseous fuel injector and a pilot fuel injector into one injector envelope.
One technique concentrically locates a pilot needle inside a gas needle, such as in the concentric needle dual fuel injection valve disclosed in U.S. Pat. No. 6,336,598, issued to Touchette et al. on Jan. 8, 2002, hereinafter the '598 patent. The gas needle is held in a closed position by the pressure of diesel fuel in a control chamber (in combination with a spring) acting on the gas needle. As used herein ‘gas’ is used interchangeably with “gaseous fuel” in this disclosure. When the fuel injector is commanded to inject gaseous fuel, a solenoid is actuated to decrease diesel pressure in the control chamber allowing the pressure of gaseous fuel in a plenum near a gas injection valve to open the needle against the reduced control chamber pressure. A match fit between the gas needle and an injector housing extends between the control chamber and the gas injection valve to reduce fluid flow between the control chamber and the plenum. A diesel fuel liquid seal is employed along the match fit, where liquid seal pressure is maintained at diesel rail pressure, which is above gas rail pressure, to prevent gaseous fuel from fluidly communicating into the control chamber when the gas injection valve is open. However, to reduce the amount of diesel fuel in the liquid seal from fluidly communicating along the match fit into the gaseous fuel at the gas injection valve, a pressure bias is maintained between diesel and gas rail pressure where diesel rail pressure is maintained within a predetermined pressure range of gas rail pressure. Certain operating modes are not possible since the pressure bias between diesel rail pressure and gas rail pressure must be maintained across all engine operating conditions. In those embodiments where control chamber pressure does not reduce to drain pressure when the fuel injector is commanded to inject gaseous fuel, it is possible that when the pressure bias is too large gaseous fuel pressure at the injection valve is not sufficient to overcome control chamber pressure preventing the gas needle from moving such that no gaseous fuel is injected.
Another technique for integrating a gaseous and pilot fuel injector integrates a pilot needle adjacent a gaseous needle in a common injector housing, such as in the side-by-side dual fuel injection valve disclosed in U.S. Pat. No. 8,839,763 issued to Mayank Mittal on Sep. 23, 2014. In this technique the gas needle is moved to an open position in a similar manner as the gas needle in the '598 patent.
The state of the art is lacking in techniques for hydraulically actuating a valve member of an injection valve in gaseous fuel injectors. The present apparatus and method provides an improved hydraulically actuated gaseous fuel injector for internal combustion engines.